1. Technical Field of the Invention
The invention relates generally to signaling within a communication network and more particularly to ACK-NACK signaling within a communication network.
2. Description of Related Art
In Long Term Evolution (LTE) and other 4G wireless communication systems, each data packet to be conveyed to the receiver (also referred to herein as “destination device”) is made up of multiple code words, which are transmitted to the receiver in a transport block. Each code word may be provided with individual Cyclic Redundancy Check (CRC) bits and each transport block may also be provided with overall CRC bits covering all code words in the transport block.
In the existing Acknowledgment-Negative Acknowledgment (ACK-NACK) signaling, the receiver returns the overall CRC status and not the individual code word's CRC status. The transport block's ACK-NACK feedback includes only a single hit in order to minimize bandwidth requirements. However, this single bit is coded heavily to ensure that the feedback information is received by the transmitter (also referred to herein as “source device”) without any error even at very low signal-to noise ratios (SNRs). For example, in LTE, the transport block's ACK-NACK after encoding may occupy about 5% of the symbol resources.
If the ACK-NACK feedback was extended to include the individual code word CRC status, each code word's ACK-NACK bit would have to be strongly coded. For example, if the number of code words in a transport block is 10, the number of resources to be used for ACK-NACK feedback would have to be increased by 10 times. In order to accommodate such a requirement, the control channel allocation would have to be increased, resulting in an inefficient usage of the bandwidth.
However, since only the overall CRC status is returned, if the receiver is unable to decode one or more of the code words in the transport block, the receiver must request retransmission of the entire transport block. For example, if the receiver is able to decode all of the code words in a transport block except one, since the transmitter is unaware of which code word was received in error, the transmitter would retransmit all of the code words in the transport block. From the retransmitted transport block, the receiver would then decode only the failed code-word.
Thus, the current ACK-NACK signaling does not inform the transmitter of which code words were received in error, so that the transmitter may re-transmit only the erroneously received code words. As such, the current ACK-NACK signaling does not efficiently utilize the bandwidth for ACK-NACK feedback and re-transmission of code words.